Local $R$-observability of differential-algebraic equations

A nonlinear system of first order ordinary differential equations is considered. The system is unresolved with respect to the derivative of the unknown function and it is identically degenerate in the domain. An arbitrarily high unresolvability index is admited. Analysis is carried out under assumptions that ensure the existence of a global structural form that separates "algebraic" and "differential" subsystems. Local $R$-observability conditions are obtained by linear approximation of the system.